The invention relates generally to data storage systems and, more particularly, to disk based data storage systems.
A disk drive is a data storage device that stores data in concentric tracks on a disk shaped medium. Data is read from the medium by spinning the medium about a central axis while positioning a transducer near a desired track of the medium to sense the data. The transducer provides an electrical signal representative of the sensed data to data processing circuitry within the disk drive which converts the electrical signal to a format that is recognizable by an attached host unit. The converted data signal is then delivered to the host unit for use thereby. Disk drives can store data in any of a number of different forms, such as magnetic data storage and optical data storage.
A seek operation in a disk drive is a process during which the transducer is moved from a present track of the disk to a target track of the disk so that a data transfer with the target track can be performed. A seek operation is generally initiated in response to a read or write request received by the disk drive from the host computer. In the read/write request, the host computer generally specifies the location on the disk (e.g., the track and sector) at which the data transfer is to take place, and the disk drive then moves the transducer to that location. Once the transducer is in position, the requested data transfer to or from the disk is allowed to occur.
Disk access time is a parameter used in the disk drive industry to specify the average time it takes a disk drive to perform a requested data transfer. As such, disk access time is ordinarily used to gauge the performance of individual disk drives with respect to other disk drives. A disk drive having a low disk access time is generally preferred over a disk drive having a higher disk access time because the drive having the lower disk access time, on average, performs read and write operations faster. Consequently, the disk drive having the lower disk access time allows the host computer to perform applications faster. As can be appreciated, the disk access time of a disk drive is directly related to the seek time of the disk drive. That is, a longer seek time will generally result in a longer disk access time.
Therefore, there is a need in the disk drive industry for techniques and devices for reducing seek time in a disk drive.
The present invention relates to a system that is capable of reducing seek time in a disk drive. In conceiving of the invention, it was appreciated that natural resonances within the actuator assembly of a disk drive are often responsible for significantly increasing the time it takes for a transducer to settle above a target track following a seek operation. The natural resonance of the actuator assembly is excited during the seek operation by impulses that are delivered to the input of the voice coil motor (VCM) of the disk drive. Once excited, the oscillations cause position errors during the seek operation that make it difficult for the transducer to properly follow a desired seek profile. Thus, a large position or velocity error exists at the end of the seek operation that the disk drive must recover from. This extends the period of time before which data transfers with the target track can be carried out.
In accordance with the invention, the control signal delivered to the VCM during a seek operation is modified to include at least one cancellation impulse that is designed to cancel oscillations excited by another impulse in the control signal. Preferably, at least one cancellation impulse is generated for each servo sample time during the seek operation. The cancellation impulse has a magnitude and timing that is related to the frequency and damping characteristics of the natural resonance. In a preferred embodiment of the invention, the cancellation impulse(s) is(are) applied during short seek operations in the disk drive. That is, the position mode tables used by the disk drive to perform short seek operations in the drive are modified to include feedforward components that can be used to generate the cancellation pulses.